About a year and a half ago, Google released the canonical tag. In summary, it is basically a special snippet of code you place on your page that does a 301 redirect without physically redirecting people, instead it redirects search bots.
In December, they expanded the use of this tag to support cross-domain canonical tag usage, as opposed to just using the tag internally. Personally, I have just used the canonical tag internally, never applied it cross-domain - yet.
A WebmasterWorld thread has Tedster saying that many, too many, webmasters are complaining about issues with the tag. He said, "in the past week or so I've read several accounts around the web of so-called "canonical disasters." He adds:
I've used the canonical link tag with no apparent problems, and in some cases it put an easy band-aid on a nasty infrastructure knot. But now I'm reading some SEO blogs that warn against serving the canonical link on the "original" URL. How could that be a problem?
I agree on that I don't see why SEOs or Webmasters would have issues with it. But I don't agree in seeing more complaints about it than normal.
In fact, in March I ran a poll asking does the canonical tag work well on Google? The response break down was mostly positive:
Not all positive. I kind of thing webmasters may not be using it right? Or maybe I am wrong?
Forum discussion at WebmasterWorld.